Birth defects of the head and face are common in the human population. Skull injuries and joint disease, in particular affecting the temporomandibular joint of the jaw, are a major economic and societal burden. This proposal is to support the upward trajectory of a mid-career investigator, Dr. Gage Crump, who works at the interface of craniofacial development and stem cell biology. Specifically, he has developed powerful new zebrafish models of human craniofacial birth defects and disease, which are allowing him to unravel the developmental causes of common craniofacial birth defects and, in a bold new direction, to understand mechanisms of stimulating endogenous repair of the adult skull. Dr. Crump is Director of the PhD Program in Development, Stem Cells, and Regenerative Medicine at the University of Southern California and a founding member of the Eli and Edythe Broad Center for Stem Cell Research, a rapidly growing institute directed by Dr. Andrew McMahon with exceptional core resources and recently recruited junior faculty. He is currently PI on three R01's from NIDCR and has published featured articles in Developmental Cell, eLife, Development, and PLoS Genetics on diverse topics ranging from craniofacial development to jawbone repair and arthritis of the jaw. He has built up an exceptional research team, with several trainees receiving K99 and F31 fellowships from NIDCR, as well as prestigious private fellowships. His previous trainees have gone on to tenure-track faculty and industry positions, and postdocs in HHMI-funded labs. He also participates in local and national efforts to recruit under-represented minority students into stem cell science from high school to graduate levels. These efforts are reflected by a USC Mentoring Award to Dr. Crump in 2017. The research program focuses on the roles of progenitor cells in building the facial skeleton and then maintaining and repairing it in the adult. These studies exploit the unique genetic and imaging strengths of zebrafish, combined with its impressive capabilities of natural regeneration as adults. The first program uses new gene editing technology in zebrafish to analyse requirements for novel craniofacial patterning genes in progenitor regulation, as well as to directly image progenitor lineage commitment using time-lapse microscopy. As exemplified by studies of Jagged-Notch signaling from fish to man, efforts to validate zebrafish findings in mouse will be performed in latter years. The second program investigates the stem cell-based maintenance of two types of joints, the sutures of the skull and the synovial jaw joint. The third program builds on innovative models of bone, cartilage, and joint regeneration in the adult zebrafish jaw, as well as a highly collaborative network of basic researchers and clinicians at USC, to understand how different types of endogenous stem cells are activated to repair craniofacial tissues. Completion of these studies will reveal commonalities and differences between the stem cells that build and then maintain and repair the craniofacial skeleton, with foundational knowledge acquired in zebrafish informing future regenerative approaches towards improving skeletal healing in patients.